The structure of a contemporary shoe includes a bottom component or outsole that is designed to interface with the ground, and an upper component or upper that is designed to interface with the foot and the outsole. Each of these components is designed with specific characteristics for enhancing the performance of that particular component and the shoe as a whole.
The shoe outsole is designed to provide a stable platform for the foot to rest on, for protection against the ground and obstacles on the ground, and to provide traction between the shoe and the surface to enable the wearer to propel, brake, and change direction. In addition to mechanical performance characteristics, the shoe outsole must also demonstrate durability and have particular resistance to wearing abrasion in order to provide the user with a reasonable outsole life.
One important characteristic of a shoe outsole is the shoe-to-surface contact and the friction that develops between these two surfaces. The existence of friction between the shoe and the ground effectively enables the wearer to move or propel himself or herself over the ground. When the shear loading of a shoe exceeds the available friction (traction) between the shoe and surface, the shoe slips over the surface. Thus, traction is important as the shoe contacts the ground, and the sheer forces increase as normal (i.e. perpendicular) loading increases. This is especially true for shoe types which place a premium on traction, such as hiking shoes, running shoes and work boots.
Consequently, and in view of all of these demands on modern footwear, shoe designers are continually looking for opportunities to increase the traction and efficiency of shoes by incorporating novel features into shoe tread materials and designs.
It will therefore be readily appreciated that there remains a need for a shoe that adjusts to uneven terrain in response to the normal loading of the shoe on rough or uneven surfaces.